feat(calendar): document outbox retention policy

tests/test_install_config.py

@@ -3,11 +3,24 @@ from __future__ import annotations
 import unittest
 
 from cryptography.fernet import Fernet
+from pydantic import ValidationError
 
 from govoplan_core.core.install_config import env_template, validate_runtime_configuration
+from govoplan_core.settings import Settings
 
 
 class InstallConfigTests(unittest.TestCase):
+    def test_calendar_outbox_retention_setting_is_validated(self) -> None:
+        self.assertEqual(Settings().calendar_outbox_terminal_retention_days, 90)
+        self.assertEqual(
+            Settings(
+                CALENDAR_OUTBOX_TERMINAL_RETENTION_DAYS="0"
+            ).calendar_outbox_terminal_retention_days,
+            0,
+        )
+        with self.assertRaises(ValidationError):
+            Settings(CALENDAR_OUTBOX_TERMINAL_RETENTION_DAYS="-1")
+
     def test_self_hosted_validation_reports_actionable_missing_settings(self) -> None:
         result = validate_runtime_configuration({}, profile="self-hosted")
 
@@ -68,8 +81,10 @@ class InstallConfigTests(unittest.TestCase):
 
         self.assertIn("GOVOPLAN_INSTALL_PROFILE=self-hosted", self_hosted)
         self.assertIn("MASTER_KEY_B64=<generate", self_hosted)
+        self.assertIn("CALENDAR_OUTBOX_TERMINAL_RETENTION_DAYS=90", self_hosted)
         self.assertIn("GOVOPLAN_INSTALL_PROFILE=production-like", production_like)
         self.assertNotIn("MASTER_KEY_B64=<generate", production_like)
+        self.assertIn("CALENDAR_OUTBOX_TERMINAL_RETENTION_DAYS=90", production_like)
 
 
 if __name__ == "__main__":